For the production of bound printed products, such as books, periodicals, magazines, etc. transport and gathering devices are well known. After collating single sheets or signatures the collated bundles have to be fed by a transport device to further processing stations such as a trimming or stitching station.
A known transport device for feeding the collated signatures from a saddle chain to a further working station uses a shuttle assembly to move the signatures to a stitching station. The shuttle assembly grips the collated signature bundle and moves it to the stitching station where it is released. Then, the shuttle mechanism returns to grip the next succeeding bundle of signatures. When the shuttle mechanism engages the next bundle of signatures, it also engages the previously moved bundle of signatures located at the stitching station and moves the bundle of signatures, which in the meantime has been stitched, to the delivery station, while the next bundle of signatures is moved to the stitching station. A transfer device and a stitching machine of this general construction is known from U.S. Pat. No. 3,317,026.
The existing systems used on many saddle stitchers use a so called reciprocating gripper system. This comprises a row of grippers which, when closed, press against the outside of the book. These grippers are connected to a "backup" bar on the inside of the book, so that one half of the book is trapped between the grippers and this "backup" bar. The grippers open, in order to release the book at the stitching station and move back in their open condition. The grippers close on moving books when they start to move forward again. In this way, they accelerate the books away from the conveyer chain and stop them at the stitching position. The whole gripper and backup assembly is supported on a linear slide and driven backward and forward by a crank mechanism.
This system, however, comprises a relatively large reciprocating mass which requires heavy support frames and a lubricated slide system. When the assembly is driven from a crank, velocities cannot easily be optimized due to the fact that a crank is only capable of simple harmonic motions. Finally, as the gripper and backup bar assembly can only contact the inner half of the book, the higher speed outside of the book is uncontrolled and this tends to cause the spine of the book to move off the saddle apex during quick deceleration resulting in off-center stitching.